Educational Lapping Facts - What are the Myths and Facts about Backlapping?

General Information
Backlapping has become a controversial practice in the field, and while Neary Tec encourages doing what is needed to maintaining high cut quality standards, we do not profess that "you have to" backlap when using our grinding system. In fact all spin grinders have the capability to do in season touch up with out the need to backlap. It should be made clear, however, that if you do choose to lap, it will not "kill your turf", it will not "ruin your bearings", and can indeed be a viable maintenance practice if conducted as intended.

FACT or MYTH: Backlapping will ruin bearings
Manufacturers choose bearings for specific applications, and the reel is typically designed for bearing loads to withstand ten times the loading, which may occur for the lapping process.
Example: A tapered roller reel bearing used for a 5" to 7" diameter reel is capable of working under a radial load that ranges from 1,200 lbs. to 1,700 lbs. The load deflection for a bedknife to pass the compound grit during the lapping process is less than 100 lbs., substantially below the load ratings of the reel bearings. It is a fact that impact spin grinding will produce a much greater radial load on bearings than lapping ever will.

FACT or MYTH: Backlapping forces water and grit into the bearings causing premature failure
The fact is that the reason people believe that backlapping causes this problem is from years past where lapping compounds were oil based and required high pressure to be washed from the reel. There are still some compounds today that do not easily rinse off the reel. However, if a good quality lapping compound is used normal hose pressure can be used to clean the reel eliminating the potential for high pressure to push water and grit past the seals in to the bearings.

FACT or MYTH: Lapping takes a lot of time and doesn't do anything
The fact is that lapping correctly is a very quick preventative maintenance practice that is very effective when performed correctly. The key is to do it in a timely manner, with reels that have been ground properly, using the proper materials, and performing the practice correctly.

The objective of a backlapping schedule is to keep the edges at an optimum, while avoiding the potential for dulling to increase to a level where grinding must occur. For this reason, backlapping modes have been put on most hydraulically driven cutting units (or it is an option) and if used in a timely manner, two minutes lap time per reel should be all that is required. As the reel wears, this lap time will increase due to more surface metal needing to be removed.

To effectively produce an even finish and to minimize the lap time as described above, the operator needs to stay with each reel for the two minute time span, and redistributing the compound to keep the abrasive material cutting at the maximum rate. If this type of practice is followed, the process is fast and effective

Four factors that effect whether backlapping will prove to be an effective practice:

1. How dull was the reel when you made the decision to lap? Remember, lapping is a preventive maintenance process. If you have let the reel go too long between lapping, then cut quality can suffer.
2. How much relief was left on the reel blade? The efficiency of the lap process will decrease as the season progresses, and if the relief has worn away, lapping will be less effective in generating an edge. If lapping a reel where relief does not exist (or a reel that has been spun ground only), there can be excessive wear on the bedknife.
3. How long you backlap? You need to lap long enough to effectively put an edge on the reel and the bedknife. "Lap" time will be dependent on how dull the reel is, how much relief is remaining, and what materials are being used to lap.
4. What is your backlapping procedure? If you do not stay with the reel for a brief period and keep the grit evenly dispersed, the quality and effectiveness of the process may not match expectations